The Orthoptics of Down Syndrome Emily A. Miyazaki, C.O.
ABSTRACT Patients with Down syndrome have many ocular anomalies. Most of them are treatable conditions that can strongly affect their quality of life if not addressed at an early age. It is important for clinicians to be aware of improvements in both the medical field and the educational systems in the assessment of these patients and in their treatment.
INTRODUCTION For many people, there is very little myth behind individuals with Down syndrome, as it is the most common, and wellknown, chromosomal anomaly. It has an incidence of 1:500-600 births. From ancient times, perhaps as long as 5000 B.C., there have been illustrated depictions of individuals with short, slanted eyelid fissures, midface hypoplasia, and protruding tongues.1 In 1866, Langdon Down, an English physician, categorized a group of institutionalized patients with these type of facial features, which he described From Saint Louis University and Cardinal Glennon Children’s Medical Center, St. Louis, Missouri. Requests for reprints should be addressed to: Emily A. Miyazaki, C.O., Saint Louis University Institute, 1755 South Grand Boulevard, Saint Louis, Missouri 63104. Presented as part of a Symposium of the Joint Meeting of the American Orthoptic Council, the American Association of Certified Orthoptists, and the American Academy of Ophthalmology, New Orleans, Louisiana, November 17, 2013.
as Mongolian in nature, with personality traits of mimicry, humor, and mental deficits. In 1959, Jerome Lejeune, following the advent of karyotyping, found that the actual cause of Down syndrome was an anomaly resulting from an extra chromosome on chromosome 21. Since that time, it has been recognized that around 95% of individuals with Down syndrome have this type of anomaly, with 3.5% resulting from a translocation defect and 2.5% from mosaicism.1-5 Many ocular manifestations have been documented in patients with Down syndrome. This article will specifically address brain development and its relationship with visual acuity, refractive error, strabismus, and amblyopia. BRAIN DEVELOPMENT In patients with chromosomal anomalies, the expression and severity of developmental delay varies among patients. In Down syndrome, specific delays and / or neurological dysgenesis are likely regu-
© 2014 Board of Regents of the University of Wisconsin System, American Orthoptic Journal, Volume 64, 2014, ISSN 0065-955X, E-ISSN 1553-4448
12
MIYAZAKI
lated by the extra chromosome, but the specific cause is unknown. In 1990, Wisniewski examined the brain development of patients with Down syndrome and compared their brains to the brains of unaffected children.6 His findings were significant in understanding the origin, location and mechanism of the expressed delays. He determined that the Down brain was very similar in both shape and size at birth when compared to normals. However, by 3-5 months of age, the anterior-posterior diameter was shorter, with reduced frontal lobes, flatter occipital poles, smaller brainstems and occipital lobes. Narrowing of the temporal gyrus occurred in 33% and a myelination delay in 22% of individuals. An overall decrease in brain mass was demonstrated more often in females than in males, and there were 20-55% fewer neurons, both lower in density and in distribution.6 VISUAL ACUITY In early literature prior to the 1980s, it was reported that patients with Down syndrome did not seem to develop, or achieve, normal visual acuity as they grew older.1-5, 7 Acuity was found to be no better than the 20 / 40 to 20 / 50 range, or worse. It was speculated that this was due to the clinician’s inability to assess vision effectively from lack of patient cooperation, decreased cognitive levels, or insufficient evaluation techniques. This insufficiency, or apparent abnormal development of vision, led Morton et al. to try an easier and more effective assessment technique.1 Using sweep visual-evoked potentials (sVEPs), which measure electrical activity generated by stimulation of the visual cortex timelocked to a visual stimulus such as a flash of light, striped, or checkerboard pattern, was very effective. They could assess vision accurately, as it only required 10 seconds of good fixation for reliable results. Further-
American Orthoptic Journal
more, the results could not only be easily correlated with Snellen acuity but also be used in identifying amblyopia. Their results demonstrated that visual acuity was near normal in Down syndrome infants, with the development of vision leveling off around 12-24 months of age. By age 2, visual acuity was significantly reduced in comparison to age-matched normal. There was no further improvement in visual acuity achieved after that age. This was an important finding, as their research verified that the decrease in visual acuity was influenced by the patient’s cognitive delays or lack of brain development described by Wisniewski and others.1, 6 Another proposed method for assessing visual function is photoscreening. In 2012, Yanovitch found this to be an effective resource in identifying ocular anomalies in patients with Down syndrome.8 It is an efficient, non-threatening, cost-effective way of assessing treatable problems in this population. They concluded that very few patients were unable to cooperate with the screening. In recent years, assessing visual acuity in patients with Down syndrome has improved. Most individuals are no longer institutionalized as they were before the 1980s. They are now raised in the home, mainstreamed in the school systems, and are given educational support. This allows them, not only to be more effective members of society, but also to be able to cooperate better with standard visual acuity testing. They are often able to identify pictures, match letters, identify numbers, and many of them can recognize Snellen letters as well. REFRACTIVE ERRORS The most common refractive error in individuals with Down syndrome has been documented as moderate to high myopia in 35-40% of patients. Hyperopia is not
13
DOWN SYNDROME
uncommon, being found in 21% of patients. Moderate to high astigmatism can also be found in 18-25% of patients, which has been considered to be secondary to increased eye rubbing from chronic blepharitis.2, 4, 5, 7, 8 In more recent literature, there has been emphasis on the importance of assessing accommodation through dynamic retinoscopy. Reduced accommodative ability, or hypo-accommodation, has been reported in 55-100% of patients.9 This is important when prescribing glasses, as many may benefit from bifocals to assist them with their near activities such as reading or working on fine motor skills. Dynamic retinoscopy is assessed when the patient is undilated, seated in the exam chair with his / her full cycloplegic refraction in place. The patient is instructed to fixate at a distance point, such as a movie or animated target to relax accommodation. With accommodation relaxed, the examiner should appreciate emmetropia, or near to emmetropia, by retinoscopy. The patient is then instructed to change their fixation point to a near fixation target, such as a sticker or small toy, either on the top of the retinoscope, or an accommodative target somewhere between the patient and the examiner. If the examiner observes an “against” movement, the patient has an intact ability to accommodate. If there is no change, and the patient stays in an emmetropic state, accommodation may be impaired. As the examiner becomes more proficient in this assessment, even if the initial response indicates a presence of accommodation, the patient’s ability to maintain accommodation can also be observed.9 STRABISMUS Strabismus is one of the most frequent finding in patients with Down syndrome and is reported in as high as 20-60% of pa-
14
tients. Esodeviation is the most common at 90%. Most are of the acquired type, such as accommodative esotropia, and very few are infantile in nature. Exodeviation is rare, occurring in 4-8% of patients and vertical deviations, secondary to fourth nerve palsies or oblique muscle dysfunction occur in 6% of cases.1, 2, 4, 5, 7, 10, 11, 12 In a long-term study from 1988-1999, Haugen and Hovding investigated strabismus in children with Down syndrome from birth to a mean age of around 4 years, with a minimum follow-up of 2 years.13 They specifically focused on the age at onset, the frequency of the type of strabismus and binocular potential. The outcome of their research found similarities to others regarding the frequency and type of strabismus. However, age at onset and binocular potential were novel findings. At age 1 year, only 5% of patients were found to have strabismus; however, by age 2, 42% of patients had strabismus. This may reflect the correlation of hyperopia with esotropia, or accommodative esotropia, manifesting at a later onset. Furthermore, of the strabismus patients, 44% had measureable stereopsis using either the Titmus Fly test or the Lang stereotest. This stresses the importance of treating the misalignment as early as possible to maintain, or recover, binocular function. With a high percentage of esotropia in patients with Down syndrome, extraocular muscle surgery is often indicated. In a syndrome that demonstrates developmental delay due to neurological impairment, many surgeons would perform conservative surgery. Over-corrections are commonly reported in children with developmental delays. However, both Hiles, in 1974, and Yahalom, in 2010, found that standard dosing for surgery does not result in an over-correction in patients with Down syndrome.10, 14, 15 Outcomes within 10Δ were achieved with normal dosing. Occasionally, there were under-corrections
Volume 64, 2014
MIYAZAKI
of esodeviations, but this may have been as a result of undiagnosed hypoaccommodation at near.
or Bangerter foils may be considered as an alternative mode of therapy. CONCLUSION
AMBLYOPIA There are many risk factors for the development of amblyopia and patients with Down syndrome. These patients should not be exempt from careful observation of their visual acuity because of their numerous and variable ocular manifestations. There are many reports that state that amblyopia is rare and not a concern in patients with Down syndrome. Most patients were reported to have very little difference in acuity between the two eyes and amblyopia treatment was rarely prescribed.1, 2, 4, 7 In contrast, however, in 1999, Tsiaras found that the prevalence of amblyopia was actually higher than previously reported.16 He observed similar findings of bilateral visual impairment of 20 / 50 or less in 46% of patients, consistent with the findings of Morton et al., but Tsiaras also found that 22% of his patients had a difference in acuity of two lines or more. This is much higher than the previously reported at 23%. He agreed with Morton et al. regarding visual acuity assessment in this population, suggesting that the lack of accuracy in both cooperation and technique could have skewed the perception of the absence of diagnosed amblyopia in the past.1, 16 Treatment of amblyopia is similar as compared to any other child with this condition. However, up to 30% of patients with Down syndrome have nystagmus, suggesting that a latent component may contraindicate the use of patching therapy. This might suggest the use of atropine therapy as an alternative. However, the use of atropine and cyclopentolate in normal dosage may be contraindicated in patients with cardiac defects associated with Down syndrome due to increased sensitivity. If unable to use atropine, optical penalization
American Orthoptic Journal
Individuals with Down syndrome may not be uncommon to our patient population, but it is important for clinicians and caregivers to be vigilant in observing and in diagnosing changes or deficits in their visual development. Early intervention is important in maximizing the potential in a visual system that is already at risk simply because of ocular anomalies, brain degradation, or other structural anomalies. It is the clinician’s responsibility to assess the patient’s vision in both innovative and in the most accurate manner. Furthermore, checking for hypo-accommodation prior to prescribing glasses is not only important in addressing their needs with near vision but also for helping these individuals in their educational endeavors and therapies such as occupational, physical, and speech. If early examination in infancy demonstrates no apparent strabismus, it is important to reassess ocular alignment between 2 and 6 years of age. Obtaining good alignment and stereopsis may contribute to their overall development. Today’s society is working to help mainstream these individuals and intervention will help them to improve not only their quality of life, but also the lives of caregivers, teachers, and therapists. REFERENCES 1. Morton GV: Why do children with Down syndrome have subnormal vision? Am Orthopt J 2011; 61:60-70. 2. Catalano RA: Down syndrome. Surv Ophthalmol 1990; 34:385-398. 3. Drack AV: Basics of inheritance. In: Duane’s Foundations of Clinical Ophthalmology. Volume 3. Philadelphia: Lippincott; 1994, chapter 52. 4. Jaeger EA: Ocular findings in Down syndrome. Tr Am Ophth Soc 1980; 158:808-845.
15
DOWN SYNDROME
5. Roizen NJ: Ophthalmic disorders in children with Down syndrome. Dev Med Child Neurol 1994; 36:594-600. 6. Wisniewski KE: Down syndrome children often have brain with maturation delay, retardation of growth, and cortical dysgenesis. Am J Med Genetics (Supp) 1990; 7:274-281. 7. Shapiro MB, France TD: The ocular features of Down syndrome. Am J Ophthalmol 1995; 99:659663. 8. Yanovitch T: The accuracy of photoscreening at detecting treatable ocular condition in children with Down syndrome. J AAPOS 2011; 14:472477. 9. Anderson HA: Static and dynamic measurements of accommodation in individuals with Down syndrome. Invest Ophthalmol Vis Sci 2011; 52:310317. 10. Hiles DA, Hoyme SH, McFarlane F: Down syndrome and strabismus. Am Orthopt J 1974; 24:63-68. 11. Becerril-Carmona AF: Alternations of ocular
16
12. 13.
14.
15.
16.
motility in Down syndrome. Am Orthopt J 1997; 47:181-188. Yurdakul NS: Strabismus in Down syndrome. J AAPOS 2006; 43:27-30. Haugen OH, Hovding G: Strabismus and binocular function in children with Down syndrome: A population-based, longitudinal study. ACTA Ophthalmologica Scandinavica 2001; 79:133-139. Yahalom C: Strabismus surgery outcome among children and young adults with Down syndrome. J AAPOS 2010; 14:117-119. Motley WW: Outcomes of strabismus surgery for esotropia in children with Down syndrome compared to matched controls. J AAPOS 2012; 49:211-214. Tsiaras WG: Amblyopia and visual acuity in children with Down syndrome. BJO 1999; 83:11121114.
Key words: chromosomal anomaly, amblyopia, strabismus, Down syndrome
Volume 64, 2014
ABSTRACT Patients with Down syndrome have many ocular anomalies. Most of them are treatable conditions that can strongly affect their quality of life if not addressed at an early age. It is important for clinicians to be aware of improvements in both the medical field and the educational systems in the assessment of these patients and in their treatment.
INTRODUCTION For many people, there is very little myth behind individuals with Down syndrome, as it is the most common, and wellknown, chromosomal anomaly. It has an incidence of 1:500-600 births. From ancient times, perhaps as long as 5000 B.C., there have been illustrated depictions of individuals with short, slanted eyelid fissures, midface hypoplasia, and protruding tongues.1 In 1866, Langdon Down, an English physician, categorized a group of institutionalized patients with these type of facial features, which he described From Saint Louis University and Cardinal Glennon Children’s Medical Center, St. Louis, Missouri. Requests for reprints should be addressed to: Emily A. Miyazaki, C.O., Saint Louis University Institute, 1755 South Grand Boulevard, Saint Louis, Missouri 63104. Presented as part of a Symposium of the Joint Meeting of the American Orthoptic Council, the American Association of Certified Orthoptists, and the American Academy of Ophthalmology, New Orleans, Louisiana, November 17, 2013.
as Mongolian in nature, with personality traits of mimicry, humor, and mental deficits. In 1959, Jerome Lejeune, following the advent of karyotyping, found that the actual cause of Down syndrome was an anomaly resulting from an extra chromosome on chromosome 21. Since that time, it has been recognized that around 95% of individuals with Down syndrome have this type of anomaly, with 3.5% resulting from a translocation defect and 2.5% from mosaicism.1-5 Many ocular manifestations have been documented in patients with Down syndrome. This article will specifically address brain development and its relationship with visual acuity, refractive error, strabismus, and amblyopia. BRAIN DEVELOPMENT In patients with chromosomal anomalies, the expression and severity of developmental delay varies among patients. In Down syndrome, specific delays and / or neurological dysgenesis are likely regu-
© 2014 Board of Regents of the University of Wisconsin System, American Orthoptic Journal, Volume 64, 2014, ISSN 0065-955X, E-ISSN 1553-4448
12
MIYAZAKI
lated by the extra chromosome, but the specific cause is unknown. In 1990, Wisniewski examined the brain development of patients with Down syndrome and compared their brains to the brains of unaffected children.6 His findings were significant in understanding the origin, location and mechanism of the expressed delays. He determined that the Down brain was very similar in both shape and size at birth when compared to normals. However, by 3-5 months of age, the anterior-posterior diameter was shorter, with reduced frontal lobes, flatter occipital poles, smaller brainstems and occipital lobes. Narrowing of the temporal gyrus occurred in 33% and a myelination delay in 22% of individuals. An overall decrease in brain mass was demonstrated more often in females than in males, and there were 20-55% fewer neurons, both lower in density and in distribution.6 VISUAL ACUITY In early literature prior to the 1980s, it was reported that patients with Down syndrome did not seem to develop, or achieve, normal visual acuity as they grew older.1-5, 7 Acuity was found to be no better than the 20 / 40 to 20 / 50 range, or worse. It was speculated that this was due to the clinician’s inability to assess vision effectively from lack of patient cooperation, decreased cognitive levels, or insufficient evaluation techniques. This insufficiency, or apparent abnormal development of vision, led Morton et al. to try an easier and more effective assessment technique.1 Using sweep visual-evoked potentials (sVEPs), which measure electrical activity generated by stimulation of the visual cortex timelocked to a visual stimulus such as a flash of light, striped, or checkerboard pattern, was very effective. They could assess vision accurately, as it only required 10 seconds of good fixation for reliable results. Further-
American Orthoptic Journal
more, the results could not only be easily correlated with Snellen acuity but also be used in identifying amblyopia. Their results demonstrated that visual acuity was near normal in Down syndrome infants, with the development of vision leveling off around 12-24 months of age. By age 2, visual acuity was significantly reduced in comparison to age-matched normal. There was no further improvement in visual acuity achieved after that age. This was an important finding, as their research verified that the decrease in visual acuity was influenced by the patient’s cognitive delays or lack of brain development described by Wisniewski and others.1, 6 Another proposed method for assessing visual function is photoscreening. In 2012, Yanovitch found this to be an effective resource in identifying ocular anomalies in patients with Down syndrome.8 It is an efficient, non-threatening, cost-effective way of assessing treatable problems in this population. They concluded that very few patients were unable to cooperate with the screening. In recent years, assessing visual acuity in patients with Down syndrome has improved. Most individuals are no longer institutionalized as they were before the 1980s. They are now raised in the home, mainstreamed in the school systems, and are given educational support. This allows them, not only to be more effective members of society, but also to be able to cooperate better with standard visual acuity testing. They are often able to identify pictures, match letters, identify numbers, and many of them can recognize Snellen letters as well. REFRACTIVE ERRORS The most common refractive error in individuals with Down syndrome has been documented as moderate to high myopia in 35-40% of patients. Hyperopia is not
13
DOWN SYNDROME
uncommon, being found in 21% of patients. Moderate to high astigmatism can also be found in 18-25% of patients, which has been considered to be secondary to increased eye rubbing from chronic blepharitis.2, 4, 5, 7, 8 In more recent literature, there has been emphasis on the importance of assessing accommodation through dynamic retinoscopy. Reduced accommodative ability, or hypo-accommodation, has been reported in 55-100% of patients.9 This is important when prescribing glasses, as many may benefit from bifocals to assist them with their near activities such as reading or working on fine motor skills. Dynamic retinoscopy is assessed when the patient is undilated, seated in the exam chair with his / her full cycloplegic refraction in place. The patient is instructed to fixate at a distance point, such as a movie or animated target to relax accommodation. With accommodation relaxed, the examiner should appreciate emmetropia, or near to emmetropia, by retinoscopy. The patient is then instructed to change their fixation point to a near fixation target, such as a sticker or small toy, either on the top of the retinoscope, or an accommodative target somewhere between the patient and the examiner. If the examiner observes an “against” movement, the patient has an intact ability to accommodate. If there is no change, and the patient stays in an emmetropic state, accommodation may be impaired. As the examiner becomes more proficient in this assessment, even if the initial response indicates a presence of accommodation, the patient’s ability to maintain accommodation can also be observed.9 STRABISMUS Strabismus is one of the most frequent finding in patients with Down syndrome and is reported in as high as 20-60% of pa-
14
tients. Esodeviation is the most common at 90%. Most are of the acquired type, such as accommodative esotropia, and very few are infantile in nature. Exodeviation is rare, occurring in 4-8% of patients and vertical deviations, secondary to fourth nerve palsies or oblique muscle dysfunction occur in 6% of cases.1, 2, 4, 5, 7, 10, 11, 12 In a long-term study from 1988-1999, Haugen and Hovding investigated strabismus in children with Down syndrome from birth to a mean age of around 4 years, with a minimum follow-up of 2 years.13 They specifically focused on the age at onset, the frequency of the type of strabismus and binocular potential. The outcome of their research found similarities to others regarding the frequency and type of strabismus. However, age at onset and binocular potential were novel findings. At age 1 year, only 5% of patients were found to have strabismus; however, by age 2, 42% of patients had strabismus. This may reflect the correlation of hyperopia with esotropia, or accommodative esotropia, manifesting at a later onset. Furthermore, of the strabismus patients, 44% had measureable stereopsis using either the Titmus Fly test or the Lang stereotest. This stresses the importance of treating the misalignment as early as possible to maintain, or recover, binocular function. With a high percentage of esotropia in patients with Down syndrome, extraocular muscle surgery is often indicated. In a syndrome that demonstrates developmental delay due to neurological impairment, many surgeons would perform conservative surgery. Over-corrections are commonly reported in children with developmental delays. However, both Hiles, in 1974, and Yahalom, in 2010, found that standard dosing for surgery does not result in an over-correction in patients with Down syndrome.10, 14, 15 Outcomes within 10Δ were achieved with normal dosing. Occasionally, there were under-corrections
Volume 64, 2014
MIYAZAKI
of esodeviations, but this may have been as a result of undiagnosed hypoaccommodation at near.
or Bangerter foils may be considered as an alternative mode of therapy. CONCLUSION
AMBLYOPIA There are many risk factors for the development of amblyopia and patients with Down syndrome. These patients should not be exempt from careful observation of their visual acuity because of their numerous and variable ocular manifestations. There are many reports that state that amblyopia is rare and not a concern in patients with Down syndrome. Most patients were reported to have very little difference in acuity between the two eyes and amblyopia treatment was rarely prescribed.1, 2, 4, 7 In contrast, however, in 1999, Tsiaras found that the prevalence of amblyopia was actually higher than previously reported.16 He observed similar findings of bilateral visual impairment of 20 / 50 or less in 46% of patients, consistent with the findings of Morton et al., but Tsiaras also found that 22% of his patients had a difference in acuity of two lines or more. This is much higher than the previously reported at 23%. He agreed with Morton et al. regarding visual acuity assessment in this population, suggesting that the lack of accuracy in both cooperation and technique could have skewed the perception of the absence of diagnosed amblyopia in the past.1, 16 Treatment of amblyopia is similar as compared to any other child with this condition. However, up to 30% of patients with Down syndrome have nystagmus, suggesting that a latent component may contraindicate the use of patching therapy. This might suggest the use of atropine therapy as an alternative. However, the use of atropine and cyclopentolate in normal dosage may be contraindicated in patients with cardiac defects associated with Down syndrome due to increased sensitivity. If unable to use atropine, optical penalization
American Orthoptic Journal
Individuals with Down syndrome may not be uncommon to our patient population, but it is important for clinicians and caregivers to be vigilant in observing and in diagnosing changes or deficits in their visual development. Early intervention is important in maximizing the potential in a visual system that is already at risk simply because of ocular anomalies, brain degradation, or other structural anomalies. It is the clinician’s responsibility to assess the patient’s vision in both innovative and in the most accurate manner. Furthermore, checking for hypo-accommodation prior to prescribing glasses is not only important in addressing their needs with near vision but also for helping these individuals in their educational endeavors and therapies such as occupational, physical, and speech. If early examination in infancy demonstrates no apparent strabismus, it is important to reassess ocular alignment between 2 and 6 years of age. Obtaining good alignment and stereopsis may contribute to their overall development. Today’s society is working to help mainstream these individuals and intervention will help them to improve not only their quality of life, but also the lives of caregivers, teachers, and therapists. REFERENCES 1. Morton GV: Why do children with Down syndrome have subnormal vision? Am Orthopt J 2011; 61:60-70. 2. Catalano RA: Down syndrome. Surv Ophthalmol 1990; 34:385-398. 3. Drack AV: Basics of inheritance. In: Duane’s Foundations of Clinical Ophthalmology. Volume 3. Philadelphia: Lippincott; 1994, chapter 52. 4. Jaeger EA: Ocular findings in Down syndrome. Tr Am Ophth Soc 1980; 158:808-845.
15
DOWN SYNDROME
5. Roizen NJ: Ophthalmic disorders in children with Down syndrome. Dev Med Child Neurol 1994; 36:594-600. 6. Wisniewski KE: Down syndrome children often have brain with maturation delay, retardation of growth, and cortical dysgenesis. Am J Med Genetics (Supp) 1990; 7:274-281. 7. Shapiro MB, France TD: The ocular features of Down syndrome. Am J Ophthalmol 1995; 99:659663. 8. Yanovitch T: The accuracy of photoscreening at detecting treatable ocular condition in children with Down syndrome. J AAPOS 2011; 14:472477. 9. Anderson HA: Static and dynamic measurements of accommodation in individuals with Down syndrome. Invest Ophthalmol Vis Sci 2011; 52:310317. 10. Hiles DA, Hoyme SH, McFarlane F: Down syndrome and strabismus. Am Orthopt J 1974; 24:63-68. 11. Becerril-Carmona AF: Alternations of ocular
16
12. 13.
14.
15.
16.
motility in Down syndrome. Am Orthopt J 1997; 47:181-188. Yurdakul NS: Strabismus in Down syndrome. J AAPOS 2006; 43:27-30. Haugen OH, Hovding G: Strabismus and binocular function in children with Down syndrome: A population-based, longitudinal study. ACTA Ophthalmologica Scandinavica 2001; 79:133-139. Yahalom C: Strabismus surgery outcome among children and young adults with Down syndrome. J AAPOS 2010; 14:117-119. Motley WW: Outcomes of strabismus surgery for esotropia in children with Down syndrome compared to matched controls. J AAPOS 2012; 49:211-214. Tsiaras WG: Amblyopia and visual acuity in children with Down syndrome. BJO 1999; 83:11121114.
Key words: chromosomal anomaly, amblyopia, strabismus, Down syndrome
Volume 64, 2014
